1. Field of the Invention
The present invention relates to a motor with a resin base plate.
2. Related Background Art
A typical motor usually has a base plate to attach the motor to other various apparatuses (i.e., main body apparatuses in relation to the motor). To enable the motor to be firmly attached to a main body apparatus and to reduce noise caused by resonance, the base plate is required to have rigidity higher than a predetermined level. For this reason, materials used for base plates in conventional motors are metals that can easily ensure high rigidity.
Metals are used for the base plate also due to the fact that a bearing holder that supports a rotor shaft in a freely rotatable manner must be fixed to the base plate and that the base plate must be able to attach the motor to the apparatus firmly.
Next, an example of a conventional motor will be described below with reference to FIG. 9. In FIG. 9, a base plate 100, which is the base of a motor, is made of a metal plate and is formed by press-forming a metal plate, for example. At the center of the base plate 100 is a cylindrical hole formed through a burring processing, and in the cylindrical hole is press fit and fixed a bearing holder 102, which is a cylinder with bottom. On the outer circumference surface of the bearing holder 102 is mounted and fixed a center hole of a stator core 106. The stator core 106 has a plurality of salient poles arranged radially, and around each salient pole is wound a coil 108. The stator core 106 and the coils 108 form a stator 104.
On the inside of the bearing holder 102 is mounted a cylindrical bearing 116, which is made of a sintered metal and impregnated with a lubricating oil. In a shaft hole formed at the center of the bearing 116 is mounted in a freely rotatable manner a rotating shaft 118. The bearing 116 is a radial bearing, and the thrust load applied to the rotating shaft 118 is borne at the bottom section of the bearing holder 102. To the top end section of the rotating shaft 118 protruding from the top end of the bearing 116 is attached a disk chucking section 120, and under the disk chucking section 120 is attached a flat rotor case 112. On the inner surface of the cylindrical circumferential wall of the rotor case 112 is affixed a plurality of drive permanent magnets 114. The rotating shaft 118, the rotor case 112 and the drive permanent magnets 114 form a rotor 110 as a unitary structure that rotates. The disk chucking section 120 rotates with the rotor 110 in a unitary fashion.
As the above description makes clear, the conventional motor in FIG. 9 forms a motor that rotatably drives compact discs (CDs) and digital versatile disks (DVDs) and that can rotatably drive a disk mounted on the disk chucking section 120. The drive permanent magnets 114 are magnetized at a predetermined interval in the circumferential direction, and the rotor 110 can be rotatably driven by switching energization to various coils 108 depending on the rotational positions of the magnetic poles of the drive permanent magnets 114.
To supply power from an external power source to the coils to drive the motor, lead wires or a printed substrate is placed between the external power source and coil terminals. However, due to the fact that the coils 108 of the stator core 106 are made of an extremely thin wire material, connection sections formed when the terminals of the coils 108 are connected with lead wires or with a print substrate tend to be unstable and lacking in strength. For this reason, various mechanisms are used to connect the coil terminals with lead wires or a print substrate in a stable manner and with high strength. On the other hand, the structure of the lead wire terminal connection section requires some ingenuity to meet demands for a smaller and thinner motor as a whole. In addition, some thought must be given to prevent stress applied to the lead wires or print substrate from spreading to connection sections and coil terminals.
In one example of a connection structure formed by coil terminals and an external circuit, the connection structure involves a print substrate provided between the coil terminals and an external power source circuit, where the print substrate has a print pattern that connects to the external power source circuit and whose one end section is fixed to a motor frame through adhesion. The coil terminals are soldered at soldering lands at one end section of the print pattern. In the embodiment described in the publication, the print substrate used is a flexible print substrate.
Another conventional example of the connection structure formed by coil terminals and an external circuit is one in which the base plate of a motor is an iron plate circuit substrate, or an iron plate substrate overlaid with a hard power source supply circuit substrate, and coil terminals and external power source circuit are connected via such a circuit substrate.
As in the conventional example in FIG. 9, the base plate 100 that serves as the base of the motor is made of metal. The reason for this is that a metal makes it easy to ensure the rigidity required, which prevents resonance during rotational drive, which in turn makes it easy to reduce noise level. Furthermore, the bearing holder 102 must be held in a unitary fashion with a predetermined strength, the perpendicularity of the bearing holder 102 against the surface of the base plate 100 must be obtained at a high precision in order to obtain a high perpendicularity for a rotating center shaft, and both of these are thought to be more easily achieved if the base plate 100 is made of a metal.
However, if the material of the base plate 100 can be replaced with a resin, the base plate 100 can be made lighter and cheaper; in addition, using a resin should make it easy to mold the base plate 100 into intricate shapes as necessary.
However, if the shape of the conventional metal base plate is used when using a resin as the material for the base plate of a motor, the required rigidity cannot be obtained due to the fact that resins have a lower rigidity than metals. This causes the resonance frequency of the base plate to be lower, which causes the base plate to resonate when the motor rotates and the noise level to be high.
Furthermore, the connection structure formed by coil terminals and an external power source circuit in the conventional motor generally involves the intervention of a circuit substrate between the two. However, since the cost of the circuit substrate itself is high, the cost of the motor as a whole increases when the circuit substrate is used.
Moreover, due to the fact that the coil terminals are placed on a flat surface of the circuit substrate after they are soldered on soldering lands of the circuit substrate, when stress is applied to the circuit substrate, the stress is also applied to the soldered sections of the coil terminals and causes the wires to break.
In addition, as shown in FIG. 9, the thrust load applied to the rotating shaft 118 is designed to be borne by a resin thrust plate 122 placed at the bottom section of the bearing holder 102. This is to reduce the wear on the rotating shaft 118. If there is no resin thrust plate 122 and the thrust load applied to the rotating shaft 118 is borne directly by the bottom section of the metal bearing holder 102, the rotating shaft 118 wears severely. The resin thrust plate 122 is placed between the rotating shaft 118 and the bearing holder 102 for this reason; however, having the thrust plate 122 causes the positional precision in the axial direction of the rotating shaft 118, as well as the dimensional precision between the rotating shaft 118 and the stator core 106 and between the rotating shaft 118 and the base plate 100, to be poor.
Additionally, the structure itself, in which the bearing holder 102 as a separate part from the base plate 100 is fixed to the base plate 100, causes the perpendicularity precision of the bearing holder 102 against the surface of the base plate 100 to deteriorate; consequently, the perpendicularity of the rotating center shaft, including the perpendicularity of the bearing holder 102, must be adjusted during assembly, which causes the assembly process to be onerous.
When fixing the bearing holder 102 as a separate part from the base plate 100 to the base plate 100 through press fit, and press fitting and fixing the stator core 106 on the outer circumference side of the bearing holder 102, the height position of the stator core 106 must be adjusted; this contributes to the onerous assembly process.